1,25-Dihydroxyvitamin D suppresses M1 macrophages and promotes M2 differentiation at bone injury sites
Samiksha Wasnik, … , Kin-Hing William Lau, Xiaolei Tang
Samiksha Wasnik, … , Kin-Hing William Lau, Xiaolei Tang
Published September 6, 2018
Citation Information: JCI Insight. 2018;3(17):e98773. https://doi.org/10.1172/jci.insight.98773.
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Research Article Bone biology

1,25-Dihydroxyvitamin D suppresses M1 macrophages and promotes M2 differentiation at bone injury sites

Abstract

An indispensable role of macrophages in bone repair has been well recognized. Previous data have demonstrated the copresence of M1 macrophages and mesenchymal stem cells (MSCs) during the proinflammatory stage of bone repair. However, the exact role of M1 macrophages in MSC function and bone repair is unknown. This study aimed to define the role of M1 macrophages at bone injury sites via the function of 1,25-Dihydroxyvitamin D (1,25[OH]2D) in suppressing M1 but promoting M2 differentiation. We showed that 1,25(OH)2D suppressed M1 macrophage–mediated enhancement of MSC migration. Additionally, 1,25(OH)2D inhibited M1 macrophage secretion of osteogenic proteins (i.e., Oncostatin M, TNF-α, and IL-6). Importantly, the 1,25(OH)2D-mediated suppression of osteogenic function in M1 macrophages at the proinflammatory stage was associated with 1,25(OH)2D-mediated reduction of MSC abundance, compromised osteogenic potential of MSCs, and impairment of fracture repair. Furthermore, outside the proinflammatory stage, 1,25(OH)2D treatment did not suppress fracture repair. Accordingly, our data support 2 conclusions: (a) M1 macrophages are important for the recruitment and osteogenic priming of MSCs and, hence, are necessary for fracture repair, and (b) under vitamin D–sufficient conditions, 1,25(OH)2D treatment is unnecessary and can be detrimental if provided during the proinflammatory stage of fracture healing.

Authors

Samiksha Wasnik, Charles H. Rundle, David J. Baylink, Mohammad Safaie Yazdi, Edmundo E. Carreon, Yi Xu, Xuezhong Qin, Kin-Hing William Lau, Xiaolei Tang

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Figure 2

1,25(OH)2D suppressed M1 macrophage differentiation but augmented M2 macrophage differentiation in vitro.

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1,25(OH)2D suppressed M1 macrophage differentiation but augmented M2 mac...
(A) RAW 264.7 cells were cultured in the absence or presence of LPS and IFN-γ. Additionally, the cultures that contained LPS and IFN-γ were added with vehicle control (VC), 10 nM 1,25(OH)2D (VD), or 100 nM 1,25(OH)2D (VD). Twenty-four hours later, the cells were stimulated with a cell-stimulation cocktail in the presence of a protein transport inhibitor cocktail overnight. The cells were then analyzed for the expressions of IL-1β and IL-12 by FACS. Data show the mean fluorescence intensities (MFIs) of IL-1β and IL-12. (B–D) Primary macrophages were generated from BM. The BM-derived primary macrophages were differentiated into M1 (LPS + IFN-γ) or M2 (IL-4) in the presence of VC, 10 nM 1,25(OH)2D (VD), or 100 nM 1,25(OH)2D (VD). Twenty-four hours later, the cells were stimulated as described in A. After the stimulation, the cells that cultured under the M1 differentiation conditions were analyzed for the expressions of iNOS, and those under the M2 differentiation conditions were analyzed for the expression of arginase 1 (ARG1) by FACS (B and C) and qPCR (D). Representative FACS plots are shown in B; MFIs of iNOS and ARG1 are shown in C; mRNA expressions of iNOS and ARG1 are shown in D. *P < 0.05, **P < 0.01, ***P < 0.001, 2-way ANOVA, n = 3.